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South Korea's Yonhap News Agency reported that the projectile appeared to be a Rodong-type, medium-range missile that flew about 620 miles and landed in the Sea of Japan within 200 nautical miles of Japan's shoreline, inside its exclusive economic zone.

The U.S. Pacific Command confirmed the launch, which included a second missile. "Initial indications reveal one of the missiles exploded immediately after launch, while the second was tracked over North Korea and into the Sea of Japan," the command said in a statement.

"[The missile launch] poses a serious threat to Japan's security, and it is an unforgivable act of violence toward Japan's security," Prime Minister Shinzo Abe said, according to The Associated Press.

North Korea's top diplomat dealing with U.S. affairs told ABC News the kind of missile launch seen on Wednesday is a direct response to the "constant nuclear blackmails of the United States and to strengthen our nuclear deterrent forces in every way."

In the first interview given by North Korea's Foreign Ministry to a U.S. television network in more than a decade, Han Song Ryol, Pyongyang's top official dealing with the U.S., said the tests were "self-defensive actions to cope with the threat from United States."

Han told ABC News' Bob Woodruff, "It is the United States who provokes. It is the United States who has conducted that kind of launch many many times. It is the U.S. who threatens DPRK [North Korea] with missiles ... All these kinds of actions tell us the U.S. is taking hostile actions against DPRK. Our rocket and missile launches take place because that is the way to defend ourselves."

In wide-ranging comments, Han said the imposition of sanctions on North Korean officials, including Kim Jong Un, "crossed a red line," and he repeated Pyongyang's claim that it regarded the sanctions as a "declaration of war." Han warned that all decisions concerning relations with the U.S. would be dealt with under wartime laws — including the detention of two Americans, Otto Warmbier and Kim Dong Chul, in North Korea. Han would not comment on the conditions of their detention and repeated that the decision to impose sanctions would have consequences for every aspect of U.S.–North Korea relations, with "no exceptions, and that includes the detained Americans."

Asked about Donald Trump's comment that he would be "willing" to consider withdrawing U.S. troops from South Korea, Han said he didn't know whether Trump said it "to be famous or more popular in the campaign, but what matters is actions." He said that North Korea strongly urges the U.S. to withdraw its "aggressive army" but that he doubts whether Trump or any other potential U.S. president would do so. Han warned that even if the U.S. withdraws its army from South Korea, "as long as the U.S. has hostile policy to DPRK, our nuclear deterrent forces will be strengthened in every way ... Irrespective of changes around us, our policy of having nuclear weapons will not change ... Our nuclear forces are a product of U.S. policy towards the DPRK. This is not an economic bargaining chip. There will be no denuclearization of Korean Peninsula on our part."